Cerium Oxide Nanoparticles Inside Carbon Nanoreactors for Selective Allylic Oxidation of Cyclohexene

Agasti, Nityananda; Astle, Maxwell A.; Rance, Graham A.; Alves Fernandes, Jesum; Dupont, Jairton; Khlobystov, Andrei N.

Abstract

The confinement of cerium oxide (CeO2) nanoparticles within hollow carbon nanostructures has been achieved and harnessed to control the oxidation of cyclohexene. Graphitized carbon nanofibers (GNF) have been used as the nanoscale tubular host and filled by sublimation of the Ce(tmhd)4 complex (where tmhd = tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)) into the internal cavity, followed by a subsequent thermal decomposition to yield the hybrid nanostructure CeO2@GNF, where nanoparticles are preferentially immobilized at the internal graphitic step-edges of the GNF. Control over the size of the CeO2 nanoparticles has been demonstrated within the range of about 4–9 nm by varying the mass ratio of the Ce(tmhd)4 precursor to GNF during the synthesis. CeO2@GNF was effective in promoting the allylic oxidation of cyclohexene in high yield with time-dependent control of product selectivity at a comparatively low loading of CeO2 of 0.13 mol %. Unlike many of the reports to date where ceria catalyzes such organic transformations, we found the encapsulated CeO2 to play the key role of radical initiator due to the presence of Ce3+ included in the structure, with the nanotube acting as both a host, preserving the high performance of the CeO2 nanoparticles anchored at the GNF step-edges over multiple uses, and an electron reservoir, maintaining the balance of Ce3+ and Ce4+ centers. Spatial confinement effects ensure excellent stability and recyclability of CeO2@GNF nanoreactors.

Citation

Agasti, N., Astle, M. A., Rance, G. A., Alves Fernandes, J., Dupont, J., & Khlobystov, A. N. (2020). Cerium Oxide Nanoparticles Inside Carbon Nanoreactors for Selective Allylic Oxidation of Cyclohexene. Nano Letters, 20(2), 1161-1171. https://doi.org/10.1021/acs.nanolett.9b04579

• Journal Article Type: Article
• Acceptance Date: Jan 24, 2020
• Online Publication Date: Jan 30, 2020
• Publication Date: Feb 12, 2020
• Deposit Date: Jan 31, 2020
• Publicly Available Date: Jan 31, 2021
• Journal: Nano Letters
• Print ISSN: 1530-6984
• Electronic ISSN: 1530-6992
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 20
• Issue: 2
• Pages: 1161-1171
• DOI: https://doi.org/10.1021/acs.nanolett.9b04579
• Keywords: CeO2 nanoparticles, Carbon nanotubes, Nanoreactors, Alkene oxidation, Nanocatalysis
• Public URL: https://nottingham-repository.worktribe.com/output/3842369
• Publisher URL: https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b04579
• Additional Information: This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b04579; http://pubs.acs.org/page/policy/articlesonrequest/index.html